The magnetic susceptibility of nickel chloride

Abstract In the course of a study of the magnetic moment of a number of complex compounds of the transition elements it was soon found that the values given in the literature for most of the common paramagnetic salts were not sufficiently consistent to enable any one of them to be used as a standard of reference. It was therefore decided to determine the susceptibility of nickel chloride in aqueous solution, since it was already known that this substance had a constant susceptibility over a wide range of concentrations. The nickel content of a solution can easily and accurately be estimated by precipitation with dimethyl glyoxime, so that a solution of nickel chloride forms a very suitable reference standard in calibrating apparatus designed for the measurement of magnetic susceptibilities. The method of measurement chosen was the cylinder method usually referred to as that of Gouy. In this method the force F which is exerted on a cylinder of cross-section A by a magnetic field of intensity H1 and H2 at the lower and upper ends of the specimen is given by F = 1/2A (κ - κa) (H21 - H22), (1) where k is the volume susceptibility of the specimen and κa that of the surrounding medium. The force F was measured by means of a sensitive balance using the method of swings, so that the specimen was displaced a few millimetres during the weighing. It was therefore necessary to design the magnet so as to give a large region of uniform field H1 and a very small value of H2. The displacement would then cause no significant change in the difference in the squares of these fields. The determination therefore involves the measurement of H1 and H2 and the determination of the cross-section of the specimen A.